If、trim、foreach
<select id="selectBooksIn" resultType="com.xhp.model.Book" parameterType="java.util.List"> select * from t_mvc_book where bid in <foreach collection="bookIds" open="(" close=")" separator="," item="bid"> #{bid} </foreach> </select>
List<Book> selectBooksIn(@Param("bookIds") List bookIds);
工具类
Pagebean.java
private static final long serialVersionUID = 2422581023658455731L; //页码 private int page=1; //每页显示记录数 private int rows=10; //总记录数 private int total=0; //是否分页 private boolean isPagination=true; //上一次的请求路径 private String url; //获取所有的请求参数 private Map<String,String[]> map; public PageBean() { super(); } //设置请求参数 public void setRequest(HttpServletRequest req) { String page=req.getParameter("page"); String rows=req.getParameter("rows"); String pagination=req.getParameter("pagination"); this.setPage(page); this.setRows(rows); this.setPagination(pagination); this.url=req.getContextPath()+req.getServletPath(); this.map=req.getParameterMap(); } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public Map<String, String[]> getMap() { return map; } public void setMap(Map<String, String[]> map) { this.map = map; } public int getPage() { return page; } public void setPage(int page) { this.page = page; } public void setPage(String page) { if(null!=page&&!"".equals(page.trim())) this.page = Integer.parseInt(page); } public int getRows() { return rows; } public void setRows(int rows) { this.rows = rows; } public void setRows(String rows) { if(null!=rows&&!"".equals(rows.trim())) this.rows = Integer.parseInt(rows); } public int getTotal() { return total; } public void setTotal(int total) { this.total = total; } public void setTotal(String total) { this.total = Integer.parseInt(total); } public boolean isPagination() { return isPagination; } public void setPagination(boolean isPagination) { this.isPagination = isPagination; } public void setPagination(String isPagination) { if(null!=isPagination&&!"".equals(isPagination.trim())) this.isPagination = Boolean.parseBoolean(isPagination); } /** * 获取分页起始标记位置 * @return */ public int getStartIndex() { //(当前页码-1)*显示记录数 return (this.getPage()-1)*this.rows; } /** * 末页 * @return */ public int getMaxPage() { int totalpage=this.total/this.rows; if(this.total%this.rows!=0) totalpage++; return totalpage; } /** * 下一页 * @return */ public int getNextPage() { int nextPage=this.page+1; if(this.page>=this.getMaxPage()) nextPage=this.getMaxPage(); return nextPage; } /** * 上一页 * @return */ public int getPreivousPage() { int previousPage=this.page-1; if(previousPage<1) previousPage=1; return previousPage; } @Override public String toString() { return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", isPagination=" + isPagination + "]"; }
stringutils
public class StringUtils { public static String toLikeStr(String str) { return "%"+str+"%"; } }
2、模糊查询
#{…}
${…}
Concat
注意:#{...}自带引号,${...}有sql注入的风险
<select id="selectBooksLike1" resultType="com.xhp.model.Book" parameterType="java.lang.String"> select * from t_mvc_book where bname like #{bname} </select> <select id="selectBooksLike2" resultType="com.xhp.model.Book" parameterType="java.lang.String"> select * from t_mvc_book where bname like ‘${bname}‘ </select> <select id="selectBooksLike3" resultType="com.xhp.model.Book" parameterType="java.lang.String"> select * from t_mvc_book where bname like concat(concat(‘%‘,#{bname}),‘%‘) </select>
List<Book> selectBooksLike1(@Param("bname")String bname); List<Book> selectBooksLike2(@Param("bname")String bname); List<Book> selectBooksLike3(@Param("bname")String bname);
resultMap:适合使用返回值是自定义实体类的情况
resultType:适合使用返回值的数据类型是非自定义的,即jdk的提供的类型
3.1 使用resultMap返回自定义类型集合
3.2 使用resultType返回List<T>
3.3 使用resultType返回单个对象
3.4 使用resultType返回List<Map>,适用于多表查询返回结果集
3.5 使用resultType返回Map<String,Object>,适用于多表查询返回单个结果集
<select id="list1" resultMap="BaseResultMap"> select * from t_mvc_book </select> <select id="list2" resultType="com.xhp.model.Book"> select * from t_mvc_book </select> <select id="list3" resultType="com.xhp.model.Book" parameterType="com.xhp.model.vo.BookVo"> select * from t_mvc_book where bid in <foreach collection="bookIds" item="bid" open="(" close=")" separator=","> #{bid} </foreach> </select> <select id="list4" resultType="java.util.Map" parameterType="java.util.Map"> select * from t_mvc_book where bid in <foreach collection="bookIds" item="bid" open="(" close=")" separator=","> #{bid} </foreach> </select> <select id="list5" resultType="java.util.Map"> select * from t_mvc_book where bid = #{bid} </select>
public void list() { // List<Book> books = this.bookService.list1(); // List<Book> books = this.bookService.list2(); List list=new ArrayList(); list.add(1); list.add(12); list.add(16); // BookVo bookVo=new BookVo(); // bookVo.setBookIds(list); // List<Book> books = this.bookService.list3(bookVo); // // // for (Book b : books) { // System.out.println(b); // } // Map map=new HashMap(); // map.put("bookIds",list); // List<Map> mapList = this.bookService.list4(map); // for (Map m : mapList) { // System.out.println(m); // // } // map.put("bid",1); // System.out.println(this.bookService.list5(map)); }
为什么要重写mybatis的分页?
Mybatis的分页功能很弱,它是基于内存的分页(查出所有记录再按偏移量offset和边界limit取结果),在大数据量的情况下这样的分页基本上是没有用的
使用分页插件步奏
1、导入pom依赖
2、Mybatis.cfg.xml配置拦截器
3、使用PageHelper进行分页
4、处理分页结果
pom依赖
<dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper</artifactId> <version>5.1.2</version> </dependency>
Mybatis.cfg.xml配置拦截器
<plugins> <!-- 配置分页插件PageHelper, 4.0.0以后的版本支持自动识别使用的数据库 --> <plugin interceptor="com.github.pagehelper.PageInterceptor"> </plugin> </plugins>
使用分页插件
<select id="listPager" resultType="java.util.Map" parameterType="java.util.Map"> select * from t_mvc_book where bname like concat(concat(‘%‘,#{bname}),‘%‘) </select>
Mapper层
List<Map> listPager(Map map);
Service层
List<Map> listPager(Map map, PageBean pageBean);
@Override public List<Map> listPager(Map map, PageBean pageBean) { if(pageBean != null && pageBean.isPagination()){ PageHelper.startPage(pageBean.getPage(),pageBean.getRows()); } List<Map> list = bookMapper.listPager(map); if(pageBean != null && pageBean.isPagination()){ PageInfo pageInfo = new PageInfo(list); System.out.println("页码:"+pageInfo.getPageNum()); System.out.println("页大小:"+pageInfo.getPageSize()); System.out.println("总记录:"+pageInfo.getTotal()); pageBean.setTotal(pageInfo.getTotal()+""); } return list; }
原文:https://www.cnblogs.com/xhpcc/p/11706167.html